Although many studies have examined the neural substrates underlying phasic alerting and spatial orienting, few have directly examined the interplay of these attentional systems within a single task. While some studies suggest that effects of these systems are additive or independent, the finding that non-spatial auditory cues improve spatial orienting in neglect patients (Robertson et al., 1998) indicates an interaction between these systems. A recent study in our lab found that a non-spatial auditory cue in a purely exogenous peripheral cueing task selectively reduced RTs to validly cued targets, suggesting that alerting specifically interacts with exogenous orienting through the mutual enhancement of sensory processing of targets. Alerting and spatial orienting may not interact under purely endogenous conditions, however, since the benefit of valid central cues may be due more to noise exclusion than to sensory enhancement. The present study directly compared the interaction between alerting and spatial orienting under otherwise identical peripherally and centrally cued conditions. Subjects viewed displays consisting of a fixation point flanked by two boxes, and identified the box in which a target appeared. Targets were preceded by one of four visual warning cues (Valid, Invalid, Double, No-Cue). The peripheral cue consisted of the brightening of one or both of the boxes, and the central cue consisted of the presentation of a symbolic letter at fixation. For both conditions, the warning cues were valid on 80% of the trials. To manipulate alerting, auditory cues were presented simultaneously with visual cues on half of the trials. Alerting was found to selectively reduced RTs on Valid but not Invalid trials in the peripheral cue but not in the central cue condition. These results confirm the interaction between alerting and spatial orienting, and indicate that this interaction is specific to sensory enhancement associated with peripheral cues.